Home Secretary Jacqui Smith today deepened her rift with Boris Johnson by declaring that she will have the final say in the appointment of the new Met commissioner.

In a letter to the Mayor, Ms Smith rejects calls by Mr Johnson for the pair to jointly interview the candidate and claims that choosing Sir Ian Blair's replacement in this way would breach rules set up to ensure a 'fair and open' selection based on merit.

In a further rebuff, Ms Smith also snubs calls by the Mayor for a delay in the appointment process, saying that a hold-up would not be in the interests of Londoners or the country, and dismisses suggestions that an overseas candidate could be chosen.

Snub: Home Secretary Jacqui Smith has rejected Boris Johnson's calls for the pair to jointly interview candidates for the new Met commissioner position

She and the Mayor had uncompromising exchanges last week over Mr Johnson's role in forcing Sir Ian's resignation.

At the weekend the Mayor wrote to Ms Smith calling for a 'fairly lengthy consolidation period' before the next commissioner was appointed.

The Mayor said that such 'a pause to take stock' would benefit the Met, while he also declared that he wanted to be inolved in both the shortlisting and final interviewing of candidates to ensure that the needs of Londoners taken into account.

But Ms Smith rejects all of his key demands.

The Home Secretary says that while she will 'have regard' to the views of the Mayor and the Metropolitan Police authority, she will make the final decision on who to recommend to the Queen after conducting the final interviews alone.

Ms Smith also rules out delaying the selection, saying it is vital for the capital and the country to fill the vacancy as swiftly as possible.

'My responsibilities for policing in London and the nation make it impossible for me to add undue delay before making a recommendation to this crucial appointment.'

The Home Secretary's letter further rejects suggestions that a foreign candidate, such as Los Angeles police chief Bill Bratton who met Mr Johnson two weeks ago, could be appointed.

'I am clear that we need an exceptional top police officer, who should be a UK citizen - not least because of the counter-terrorism sensitivity of the post'.

Ms Smith says that among the qualities that will be required of the successful candidate are the ability to provide leadership on key issues such as counterterrorism, equality and diversity and building public confidence.

Adverts for the vacant post are expected to be placed shortly and an initial shortlisting and interview process will be carried out by Home Office Permanent Secretary Sir David Normington, the director general of Office for Security and counter-terrorism charles Farr, two members of the MPa and one more independent person.

Ms Smith says that following this process, Mr Johnson and the MPa will be able to 'form your views' and pass them to the Home Office, but she will take the final decision.